KevinRum

Gas mileage difference is better than you think. In most cases the cost savings between the E85 and higher ethanol blends end up being a wash due to the poor gas mileage of the higher ethanol. 53 cents is a rather large margin to make up though.

Yup, Shark Fin gasket as rav3 pointed out!

I'm with you Mike! Just sent my 2014 to the shop this morning for a transmission. Spent most of this summer in and out of shop with 4x lifter failures and an oil pump. I will have spent >$13K on repairing my truck this year, wondering why I ever sold my 2000 Sierra:( Sounds like you have a good plan though.

No, the oil pump was the start of my issues as I was getting a faulty oil pump message before any lifters blew. Despite showing the 2-stage oil pump error, I was seeing high pressure albeit somewhere a little past 80psi and low side was about 17psi at idle and warm. It did not seem the "span" of the truck gauge was inaccurate since I was extreme on both ends and the new gauge read the same. When the mechanic put a master gauge in-line he supposedly saw pressures all over the place and determined the pump needed replacement. Interesting fact is the pump error would almost always pop up while cruising down the highway at 40psi, which is technically when the VLOM is supposed to activate! It never popped up at idle when the pressure was low. After replacing the pump, the pressure increased a few psi on the low end and would spike way past 80+. The gauge would hit 80psi hard and quick which is why I think they were around 100psi since the gauge does not go that high. Hind site, I think the VLOM was my main issue and the pump still had some life in it. Also note before the oil pump was replaced, I could keep the pressure at or slightly below the 80psi mark depending on the rate I applied load when the truck was hot. When it was not fully hot, it was almost a guarantee it would exceed 80psi at 3500rpm, so there were times I too could keep below the 80psi mark. If I were you I would change the VLOM and then go from there.

FYI: My Sierra did not have a screen under the pressure sensor, and according the the dealer and my VIN, it does not come with one. Changing the pressure sensor made no difference on anything.

Hi RustyGunz, That is correct, the top pressure I now see is 75-78psi with petal to the metal. Low side is still the same before and after the high pressure situation. I am leaning more toward the new VLOM fixed that issue - I think the old one, despite testing fine, was a little sluggish not visible during static testing. Technically the AFM should not activate under load so I don't know. I can say I babied my ride almost every time I got the truck back, very careful not to let the pressure get too high and still failed within 100miles every time. I too was looking hard at putting a for sale sign on mine but knew I would feel bad if it happened to the next person. With the price of new and used trucks, I just couldn't afford it this year. I even contemplated a trade in on another brand but it simply wouldn't stay running long enough to make that happen. I feel your pain and wish you the best whatever you do!

Hi RustyGunz, I am no mechanic so take my experience with a grain of salt. I can attest to having the exact same issue and no-one would grasp the severity of the massive amount of pressure I saw on my gauge. I swear if the gauge could read 100psi, it would be there and get there almost instantly when reaching 3000-3500rpm. My low side was around 25psi at <1000rpm when hot so the range of the sensor was not skewed per se. A new pressure sensor measured the exact same thing by the way as it was one of the first things I tried. Did I mention this was after a brand new Oil pump was installed so can't blame the issue on that. It wasn't until the 4th failed lifter (replaced all of them the first round) did my mechanic change the VLOM (and pressure bypass in the 2-stage oil pump housing/system - so he said). I don't know for sure if he actually changed the pressure bypass but the GMC Dealer mechanic I was also corresponding with was certain the high oil pressure was from the VLOM. When the new lifters failed, they were destroyed - mechanic said he never saw anything like it, even mentioned it looked like they exploded! Also, it was a different lifter every failure. Once the pressure subsided (always less than 80psi) , no more lifter failures. I'm not sure which fixed the issue and my prior suggestion with the AFM bypass was because I felt every failure I had was due to the AFM trying to kick in and the VLOM too sluggish to respond in time. I thought it might save you from repeated failure until you saw that pressure go back to normal.

RustyGunz, I went through the exact same issue 4 times over and basically without my truck for 3 months. I had to demand the mechanic change the VLOM and the pressure relief valve before the high pressure and failed lifters went away. Mechanic said with every failure "higher pressure is better than lower". In the end he was sucking on that higher pressure as he had to cover the cost of each failure after the first. If I were to go through it all again, I would change the VLOM and get a plug-in AFM Bypass module and see if your pressures subside. If not, you will be into removal of the oil pan and possibly oil pump. Good luck and let us know how it goes. Note: The dealer, who I was conversing with through my difficulties, was certain the high pressures were the result of a faulty VLOM.

Glad you were not stuck like I was. Note: Neither of my vehicles this problem occured had remote start.

Hello Ccote, I have had a similar issue with two of my past vehicles (2000 Sierra 1500 and 2004 Impala, 3.6l). I never found the issue with the Sierra, but the Impala grew to such a big problem the shop replaced and reprogrammed the main computer which fixed the issue. I always figured the issue was a bug in the software and more specifically within the security system. I wish you luck in finding it because it is very elusive.

Thank You newdude! That makes sense and great information. I will forward this to the mechanic as I am still waiting for it to be repaired for the third time. They now say the part or on backorder because there is a shortage in the area ... go figure!

Sorry, misfires on cylinder 6 and 1, not five. They said the VLOM was tested and met specifications, but not replaced. Not sure if I mentioned the oil pressure sensor was replaced early in these issues. Is the pressure control solenoid different than the pressure sensor and where is it located? I doubt the pressure control solenoid was changed but considering I have very high pressure, it would seem the 2-stage pump is kicking in ... but beyond my knowledge base. Also, the tensioner was not part of the parts RR list so doubt that was replaced either. Thank you for your help and input!

Hello Everyone! I seem to have a compounding issue with my 2014 GMC Sierra SLT 5.3L which I have been the owner since 2016. It started about 7 weeks ago with an oil pump failure code appearing often although always had oil pressure, in fact it would fluctuate between 18psi at stop light to almost 80psi when accelerating very fast. Took 3 weeks to get into mechanic and drive it carefully during this time resetting the code each time it showed up (each leg to and from work, 28miles). After mechanic connected his master gauge, he said pressure was all over the place so recommended replacing the oil pump. Once replaced, no more error codes although my pressure still fluctuated between 18psi and now buries the needle way past 80+ psi when under high load. If the gauge went to 90 or so I felt like it would still bury it. Mechanic said high pressure better than low although in the 160K miles already driven, I have never seen it reach much over 70 psi even while pulling the camper … until the 2-stage oil pump error code. This is just the beginning folks. Not a week passed and started getting random misfire code. Since it was rainy when this occurred, we figured it was plugs or wires. Code went away on its own while on my way to the parts store (rain cleared up and now sunny), purchased and changed them anyway. No problems for few days till it snowed Easter evening. The next morning while leaving for work, misfire cylinder 5, so I turned around and quickly installed the new coil pack. This did not fix issue. Drove to work with misfire then had it towed to the mechanic so I wouldn’t complicate the issue. Problem was a collapsed lifter, intake side. Mechanic replaced all lifters. Drove less than 100 miles and misfire cylinder 5 again! Immediately towed back to the mechanic who verified exhaust lifter (new) failure. In fact, mechanic said it was destroyed. Mechanic replaced that lifter under GM parts warrantee and in less than another 100 miles, misfire cylinder 1. Just before this latest lifter failure (so I assume) I read an old code P0451. Q: Could the P0451 have anything to do with my lifter rash and what the heck is the mechanic missing about all these failures? I really think the large change in oil pressure, even before the new pump, is key to what might be causing the lifter failures, but the mechanic keeps dismissing it. Can anyone help me understand?